Do you think that Pol Pot and Joe Stalin would have killed just as many people if they were theists?
Yes. Yes, I do. In fact, I think they would have killed many more, much faster, and with more support from their populations. They were nut-jobs.....and it was only their atheism that prevented them being much, much worse. And it seems you agree.
Theism in itself is not noble or grand. It can be just as hideous, or more so, than atheism in my eyes. Belief in a god or gods doesn't mean someone is morally superior to someone who is an agnostic or an atheist.
But the question you have been continually avoiding is why you want to establish causation between "atheist" and "mass-murder", without any attempt to show anything beyond (possible) correlation.
Like plethora said - Stalin killed millions. But did he kill millions because he was:
A) An atheist?
B) A Russian?
C) Had a moustache?
D) Ate cabbage?
Unless and until you can show that he killed because of one of those (or another) reason, there is no more sense asking "why did the atheist kill....?" than "why did the sushi-lover kill....?".
And I know you don't want to discuss it - and I can see why - but the reverse it not true: all to often we can say "why did the believer kill....?" precisely because
of their belief.
So go ahead: explain why all the deaths these people caused were caused because they were atheists. Or are you just trolling?